This invention relates to positive displacement fluid devices such as fluid-driven motors and pumps which are operable for pumping high temperature, and contaminated fluids. More particularly, such a fluid device is a circumferential piston pump or motor configured for multi-chambered use in stacked and multi-stage operation.
Conventional methods and apparatus for bringing well fluids to the surface involve various pump systems of different designs and methods of operation. Restrictions on existing pump systems sometimes include dimensional constraints, the ability to handle high temperature and the need to pump contaminated fluids, e.g. high sand content particularly at high temperature. Conventional pumps are limited by their use at high temperature and with contaminant sensitive polymers.
Further, pumps having rotating components must have some form of bearing to separate the moving from the stationary components. It is a constant challenge to maintain bearing integrity in high temperature or contaminated environments. Such environments include those typical in the recovery of high temperature hydrocarbons from Steam Assisted Gravity Drainage (SAGD) wells in the heavy oil and bitumen recovery of northern Alberta, Canada.
In downhole operations, such as conventional oil recovery operations, progressive cavity (PCP) pumps have been applied to great effectiveness. However, as the well becomes deeper, as the temperature increases, and as the level of contamination increases, the elastomers used begin to fail resulting in pump failure and more frequent and expensive turnovers.
As an alternative, one may consider positive displacement pumps which are applied in food and other fluid industries. Among this class of pumps are circumferential piston pumps which have been known since at least 1935 in U.S. Pat. No. 2,096,490 to Hanson and still in production today by Waukesha Delavan, Wis. (Universal II Series) and Tuthill of Alsip, Ill. (HD Series). Conventional circumferential piston pumps utilize opposing, contra-rotating rotors having pistons which are alternately swept through a common chamber. Timing gears coordinate the rotor rotation. Traditionally used in surface applications, significant effort has been applied in order to seal the rotation of the rotors and the resulting pumps to date have been typically used in single stage applications. The rotors are each fitted on a shaft rotatably supported on bearings, either cantilevered or being fit with bearings at each end. The bearings are lubricated and separated from the process fluids by seals (commonly known as external bearings).
The usual approach for increasing the volume and fluid flow rate from such positive displacement pumps has been to increase the pump""s dimensions. However, in the restricted space of a wellbore, such dimensional scale-up of pumps is not suitable for providing either the necessary pressure or the flows in the wellbore.
In some applications, such as hot, contaminated downhole wellbore operations, there is an objective to increase either the volumetric flow rate or to increase the output pressure beyond that which can conventionally be provided using a conventional circumferential piston pump. Conventional pump technology has not fulfilled these objectives. The design challenges are further increased where the fluid is hot and contaminated, further affecting the challenge of sealing the rotors of such pumps. In particular, in the high pressure, high temperature contaminated environment of oil well downhole operations, there is little opportunity to provide an optimum environment for the bearings.
The above problems and challenges are equally applicable to the reverse operation in which fluid is forced through such devices so as to drive a shaft and act as a motor.
Accordingly, there is a need for a fluid device which can operate in high temperature, contaminated fluids and which can be further adapted to operate in high volume and pressure operations, even in such restricted spaces as a wellbore.
The invention provides an improved positive displacement fluid device, such as a pump, having one or more pump sections, the pump sections being adapted for axial stacking which enables high volume, high pressure transport of high temperature production fluid which can contain a substantial degree of contamination. The novel pumping system overcomes the high temperature limitation as well as being associated with a high tolerance to pump contaminated fluids over a wide viscosity range. The capability to pump high temperature, contaminated fluids is achieved using a circumferential piston pump utilizing a novel sealing arrangement. Further, pump sections are stacked in parallel to achieve required flow rates. The parallel stacked pump sections are in turn stacked in series to meet required discharge head or pressure. Configured as a pump, the fluid device is driven by a drive shaft for pumping fluid. Configured as a motor, fluid is forced through the sections for turning and driving the shaft. Herein, the specification concentrates on a description of the fluid device as a pump although the principle and inventive concepts apply equally to a motor configuration.
In a preferred pumping configuration, the invention is a multi-chamber positive displacement fluid device or pump comprising two or more stacked positive displacement pump sections, each pump section having a rotor chamber for pumping fluid from an intake adapted for communication or connection with a fluid source to a discharge manifold and through a fluid discharge adapted for communication or connection to a fluid destination. Each rotor chamber contains rotors driven by common timed drive and idler shafts extending axially through each stacked rotor chamber. Each of the stacked sections has a common discharge manifold which contributes its incremental flow to the common discharge manifold. The sections can be stacked in any combination of parallel or series arrangements, each of which utilizes a drive shaft which extends co-axially through the stack of sections.
If the sections are stacked in parallel, the volumetric flow rate is incrementally increased.
If the sections are stacked in series, the discharge pressure capability is incremented. For a series arrangement, the discharge of one section or stack of sections is fluidly connected to the inlet of a successive stacked section through a crossover section. Sections stacked in series with a cross-over form a pumping stage for incrementally increasing the pressure at the fluid destination.
Applied as a motor for a given flow rate of fluid, sections stacked in parallel result in a greater torque at the drive shaft and sections stacked in series result in a greater rotation speed.
In a multi-section pump, the invention comprises: two or more axially stacked pump sections, each section having a rotor chamber and associated rotors for pumping fluid from an inlet to a discharge manifold and a drive which extends axially through each rotor chamber for rotating the rotors and pumping fluid. Each section comprises a pump housing for housing the rotor chamber and rotors which are sandwiched between end plates and seals.
In a multi-stage pump, the invention comprises: a suction stage have having one or more axially stacked suction pump sections, each section having a rotor chamber and associated rotors for pumping fluid from an inlet to a discharge manifold; and at least one pressure stage, each stage having one or more stacked pressure pump sections, each pressure pump section having a rotor chamber for pumping fluid from a suction manifold to a discharge manifold; a crossover section for fluidly connecting the discharge manifold of the suction stage to the suction manifold of the pressure stage; and a drive which extends axially through each rotor chamber for rotating the rotors and pumping fluid.
More preferably, the drive comprises a drive shaft or a plurality of co-axially connected drive shafts extending axially and rotatably to the rotor chamber of each section for rotating one of the rotors; an idler shaft or idler shafts extending rotatably to each rotor chamber for rotating the other rotor; and timing means between the drive shaft and idler shaft for contra-rotating the rotors.
The entire stack of sections and crossovers between stages can be fit into the bore of a tubular barrel, compressed sealably together and retained therein, the barrel forming a pump having a fluid intake or inlet ports to a suction stage and having a fluid discharge from a pressure stage.
Such a pump has great versatility in its designed flow capacity and lift, all of which can be assembled into a small diameter package and which is driven through a single drive shaft connection; ideal for downhole operations or other space restrictive areas. Configured as a motor, the fluid device demonstrates similar same space and performance advantages in meeting desired output torque and rotational speed characteristics.